TOPOGRAPHIC LINEAMENTS AND EXPRESSION OF FRACTURE ARRAYS IN THE EDELMAN AND NORTH PAINT ROCK CREEK LINEAMENTS, BIGHORN MOUNTAINS, WYOMING

By Chad Trexler

Whitman College, Walla Walla WA

The geologic structures of the Bighorn Mountains in north-central Wyoming resulted primarily from tectonic forces associated with the Laramide mountain-building event that occurred 70 to 80 million years ago. Compressional forces associated with this event produced sets of well-exposed fractures in the sedimentary rocks of the Bighorns. The underlying crystalline basement rocks contain fractures of many ages and orientations that are related to multiple episodes of deformation that began as much as 2.5 billion years ago. Analyses of the fractures in these older rocks using geographic information systems and the tools of geomorphology and structural geology illuminate the role of the basement rock in the uplift of the Bighorn Mountains as a response to Laramide compression.